Spark plug and method of making the same



Dec. 7 1926.

H. RABEZZANA SPARK PLUG AND METHOD OF MAKING THE SAME Filed August 9,1922 .llnlll i )s A@ ,4

Patented Dec. 7, 1926.

UNITED STATES HECTOR RABEZZANA, OF FLINI, MICHIGAN, ASSIGNOR '.LO ACSPARK PLUG l 1,609,735 PATENT OFFICE.

COMPANY,

OF FLINT, MICHIGAN, A CORPORATION OF MICHIGAN.

SPARK PLUG METHOD OF MAKING THE SAME.

Application led August 9, 1922. Serial No. 580,751. Y

My invention relates to spark plugs of the single piece type or varietywherein the porcelain or equivalent material insulating member which'carries the' central electrode 6 is permanently held in place withinthe hollow metallic shell or casing which carries the outer or groundedelectrode of the plug by an. inturned flange at the outer end of saidshell, and which flange is forced into 10 holding engagement with theinsulating member .during the manufacture of the plug; and the principalobject of my invention is to provide a plug of the type referred towherein the insulating member will be less likely to be injured, Aas bycracking or unduly straining the same, during the secur- `ing of thesaid member in place within the casing than has heretofore commonly beenthe case; with a resulting reduction in the 2`0 number -of imperfectplugs due to injury to the insulating members thereof during theassembling of the plugs. y

A further object of my invention is to provide a spark plug of the typereferred to and wherein the insulating member will be heated less duringtheassembling thereofwithin the supporting shell than has heretoforecommonly been-the case; this result being due'lfor the most part to thefact that the holding flange which holds the insulator in place may beforced into holding engagement therewith without heating said flange Yat all, or by heatingv it much less than has heretofore commonly beenthe case, as well 36 also as to the further fact that the portion vofthe shell or casing which is heated to insure gas tight joints betweenthe .shell and insulating member (due to contraction of said heated partlas it cools) is a portion 40 which is not in intimate contact with thein` sulating member, and is/a portion which may in fact be spaced asubstantial distance from said insulating member.

A further object of my invention isi` to,y

provide a single piece or permanently as sembled plug which may bemanufactured at less cost than heretofore as the comparatively expensivedies employed in vturning a flange of the shell inward and into holdingengagement with the insulating member will last much longer than hasheretofore been the case; this being due to the fact that the die whichaccomplishes such inturning of the holding flange acts upon acomparatively cold part of the shell or casing, and is nota securing ofthe insulating members within the external casings thereof ashereinafter explained, as well also as a plug having the features. ofconstructionQ hereinafter enumerated;v and is so ,claimed and intendedto be patented in this application.

In the drawing accompanying and forming a part of this specificationyand wherein the preferred embodiment of my invention is illustrated:

Figure 1 is a view partly in section and partly in elevation showing aninsulating member in place within the shell or'casing of a plug, theannular ribof the shell not having been turned into holding relationwith the insulating member.

Figure 2 is a` similar view showing the plug wholly' in section upon alongitudinal central plane, the rib of the shell having been turnedinward and into permanent holding vengagement with the insulatingmember.

Figure 3 is a view showing the plug in section as in Figure 2, andshowing also in va conventional manner one form or type of dies whichmay be used for performing one ofthe steps necessary in assembling theplug.

Figure 4 is a view similar to Figure 3 and showing, conventionally, howa portion of the shell of the plug may be heated electrically inperforming the final step of securing the insulating -member in place inthe shell.

Figure 5 is a view upon alarger scale showing a section upon atransverse plane indicated by the line 5 5, Figure 2.

Referring now to the drawing, the hollow metallic shell or casing 6 ofmy improved spark plug is shown as provided with the usual threaded endportion 7 to be screwed the assembling of the parts in the manufactureof the plug, as shown at 11 in F igures/ 3 and 5, to thereby provide aholding flange which holds the insulating member permanently in placewithin the casing of the plug. The insulating member illustrated is onehaving an enlarged central portion 12 and shoulders 13, 14 at the lowerand upper 15 ends of said enlarged portion; the former overlying andbeing supported upon an annular ledge 15 within the shell while theinturned holding flange overlies the latter of said shoulders. Suitablegaskets are commonly placed between the shoulders 13, 14 and the ledge15 and holding flange 11 as shown, and as is usual in spark plugs of thepermanently assembled or single piece type to which my inventionrelates.

The shell or casing is provided with a circumferentially extendinggroove 16 whereby a comparatively thin wall section 17 is provided, saidgroove and wall being located between the shoulders 13 the two jointsbetween the shell'and the insulator; the joints as will be appreciatedbeing formed one by the ledge 15, the lower shoulder 13 and by thegasket commonly interposed between said elements and the '35 upper bythe upper shoulder 14, the holding ange 11 and a similar gasket. Thegroove is illustrated as agonal wrench receiving portion although it isobvious that this relationship of the elements in question may bevaried, so long as the groove and wall section at the bottom thereof arebetween the joints which prevent leakage of gas from within the cylinderof the engine with which the plug is used through the plug between theinsulating member and the shell or casing thereof.

The enlarged cent-ral portion 12 of the insulating member 10 ordinarilylits quite loosely in the internal cavity or space of the 59. shell; sothat the interior of the shell at or vadjacent the wall section 17 andthe periphery of the insulator are not in very intimate contact with oneanother, and. indeed there is commonly quite an appreciable space 5"about the enlarged central portion of the'insulator; so that the flow ofheat from the shell to the insulator when the wall section is heated aswill hereinafter appear will be reduced to a minimum as there is a gap,or

at least a portion of poor heat conductivity,

4in the path through which heat flows to the insulating member.

The central electrode 18 of the plug eX- tends through a passageprovided in the insulating member 10 while the outer or and 14 andbetween located in the hex-v wlse secured'tto the inner end of the shell6, y

as is usual in spark plugs; although the form.-

arrangement or other features of the electrodes are in no way involvedin thispresent invention and may belvaried without departing therefrom.

In assembling-my improved spark plug the insulating member l() alongwith such gaskets as may be required is placed within the hollow shell 6and the annular rib 9 at the upper enoll thereof is turned inward toprovide the holding flange 11; which turning in operation may beperformed by the use of any suitable machine, tool orv device such, forexample, as by the dies 20, 21, Figure 3, of a suitable press. Thisoperation is commonly performed at ordinary or room temperature, thatis, the rib 9 of the 'shell is not heated prior to or duringthe'tu'rning in operation, as has heretofore commonly been the case;fromwhich it follows that the die 21 which performs such operation willhave a long life, as it operates always upon cold metal and is notheated to any appreciable degree by the article upon which it operates.

This inturning of the holding ilange 11 secures the insulatorin placewithin the-shell andinasmuch as the gaskets at the joints between theshell and the insulator are necessarily compressed to some extent duringthis operation, results in tightness to a degree at the said joints;although the joints thus formed are not so perfect as are necessary orat least desirable in the finished plug to prevent leakage of gastherethrough.

After the insulating member has been ser cured in place as aboveexplained the` plug is placed between the conventionally shown terminals23, 24 of a suitable electric welding machine, see Figure 4, and currentsufficient in volume to soften the thin annular wall section 17 ispassed through the casing 6 simultaneously with the application ofpressure thereto through the terminals of the machine; During-this stepthe said wall yields under the pressure transmitted thereto from the'machine terminals through the more massive and unheated end portions ofthe casing upon' either side of the groove 16. t e gaskets arecompressed to an extent such that gas tight joints are" secured betweenthe external shell and the insulating lmemberI contained therein, andall parts adapt themselves to one another and assume the fixed positionswhich they occupy7 in the finished plug. ,Then and upon the interruptionof the flow of current the heated wall at the bottom of the grooveVcontracts and presses the gaskets thusproviding a plug in which thefinal pressure is due to the contraction of a heated portion of themetallic shell thereof, but in which little or no heat has beencommunicated to the insulating further, comllO member' thereof; as theholding flange 11 has not been heated at all, and the heating of thewall section 17 has been for a short time only.- Finally, the wall beingcommonly spaced slightly from the central portion of the insulatorcommunicates little or no heat thereto; and such heating as may occur isof a massive part of the insulator remote from the joints where heatingwill be the least harmful, The heat of the wall Section 17 is rapidlydissipated throughout the massive end portions of the `Vshell upon eachside of the groove aforesaid when the flow of current is interrupted,thus obviating local heating of the insulator and distributing thestresses incident to the assembling of the plug more uniformlythroughout the entire Structure thereof than has heretofore been thecase in single piece spark plugs.

While in explaining my invention I have referred to the steps of turningthe holding flange 11 inward, and of heating the thin wall 17 andsubjecting the shell to the final compressing action of the terminals23, 24,

as performed by separate devices, these two operations may, if desired,be performed by one and the same machine.A In that case dies theequivalent of the dies 20, 21 are insulated from one another and'constitute the terminals of an electric. machine of the riveting orwelding type, and a current of electricity of suflicient volume to heatthe wall 17 to the requisite degree will be caused to flow through thebody and wall after the holding flange is turned inward to secure theinsulating member in place within the shell. The turning in of theholding flange should as a matter of course be accomplished before thewall 17 becomes heated to such a temperature as to yield appreciablyunder the pressure due to the inturning of the holding flange; and thesupply of heating current may, if found necessary or desirable, bedelayed somewhat to secure the Icomplete inturning of said flange beforeany current flows through the dies acting as terminals and. the shell ofthe plug.

As a matter of course the pressure exert-ed by the terminals will bemaintained during the heating of the wall 17 in order that said wall maybe compressed while in a softenedy and yieldable condition, and theparts of the plug made to assume their final positions, after which andas the wall contracts the joints are subjected to a final grippingaction as hereinbefore explained.

Having thus described and explained my invention I claim and desire tosecure by Letters Patent: i

1. A spark plug comprising ahollow metallic shell or casing, and aninsulating member permanently held in place therein between two jointsspa`ced apart from one an- 'otherg the wall of said casing between said`joints being reduced in area throughout a part of its length, and thethin wall portion thus produced having been compressed during themanufacture of the plug to a degree sufficient to produce yie ding ofsaid thin wall section, to thereby insure enhanced tightness at saidjoints.

2. A spark plug comprising a hollow metallic shell or casing, and aninsulating member-permanently held in place therein betweentgwo joints saced apart from one another; the wall o said casing between said jointsbeingreduced in area throughout a part of its length, and the thin wallportion thus produced having been heated under pressure applied thereto,and permitted to, contract, during the manufacture of the plug, tothereby insure enhanced tightness at said joints.

3. A spark plug comprising a hollow metallic shell or easing and aninsulating member permanently held in place therein between an internalsupporting ledge of the casing and an inturned holding flange integralwith the casing and engaging said insulating member, a .portion of sa1dcasing between said ledge and holding flange having been compressedsubsequent to the inturning of the flange aforesaid into holdingrelation with said insulating member to a degree sufficient to produceyielding of said intermediate portion.

4. A spark plug comprising a hollow metallic shell or casing and aninsulating .member permanently held in place therein between an internalsupporting ledge of the casing and an inturned holding flange integralwith the casing and engaging said insulating member, and which shell isgrooved between said ledge and said holding flange to thereby-provide acomparatively thin wall section at the bottom of said groove and betweensaid elements; said thin wall section having been heated and compressedsubsequent to the inturning of the flange aforesaid into Iholdingrelation with said insulating member. v

5. The method of making a spark plug which consists in providing ahollow metallic'shell or casingr having an internal supporting ledge, arib at its upper end. and an external circumferentially extending groovebetween said rib and said ledge; placing an insulating member withinsaid casing and turning said rib inward and into permanent holdingengagement therewith; and thereafter applying pressure to the portionsof said casing separated by said groove to thereby compress thecomparatively thin wall section at the bottom ofvsaid groove to a degreesufficient to produce yielding of said thin wall section.

6. The method of making a spark plug which consists in providing ahollow Inetallic shellor casing having an internal supporting ledge, arib at its upper end, and an external crcumferentially extending groovebetween said rib and sald ledge; placmg an insulating member within sa1deasing and turning said rib inward and into permanent' 5 holdingengagement therewith; and thereafter heating the comparatively thm wallsection at the bottom of said groove land HECTOR RABEZZANA.

